neovibe troubleshooting - not working correctly

[larsthestrat]

it starts right away from the input (audio probe), whether it's on or off, there's this beep. When disconnecting C17 the beep is gone and I have a clean signal. So the first stage seems fine.

[R.G.]

If it's present at the input, then the input is included in the feedback loop that's letting it oscillate. This is possible a couple of ways, one being a soldering/component flaw on the PCB, but a mistake in wiring is far more likely. I would start with (re)checking that.

[larsthestrat]

thanks, could you please check the wiring in the pics I posted. I checked and double checked, I can't find any mistakes (but I'm a beginner in DIY). I can make new pics if it's necessary.

[larsthestrat]

okay, it looks like there's somethinh incorrect between the schematic and the wiring diagram. on the wiring diagram it seems that the wire from dpdt to PCB is connected to A1 (first lug of A1, A and B), shouldn't that be to A (this is what the the schematic says). Please confirm (and if so are there any other flaws in the wiring diagram?)

[larsthestrat]

anyone??

[Liquitone]

when looking at the pictures I noticed C4 is a bigger size cap than C5,. I would expect the 330pf C4 to be smaller in size than the 0.015uf cap.
As there seems to be a problem with Q3 could it be possible you've swapped them around?

[larsthestrat]

thanks:
C4 says Wima 330/100
C5 says Wima 0,015/100

[Liquitone]

Ah, no mistakes there then.I would have expected a wima fks to be smaller than a mks.

[Liquitone]

p.s. your wiring also seems to be correct.

[larsthestrat]

Thanks. I did changed the wire going from dpdt to A1 (first lug) to A second lug as proposed in the schematic above. Now the loud beep is almost gone when the effect is not engaged.
So is there a fault in the wiring diagriam?

[larsthestrat]

mr. R.G. Keen (or anyone else) could you help me out?

[larsthestrat]

update: squeeling noise is fixed, the trimpot on R35/R36 was a 500 ohm trimpot instead of 200k. I just used 2 x 100K resistor and now I have a normal signal.
No effect yet because the lamp is just glimmering (not enough voltage on that one I guess). Is it better to use a larger trimpot on the lampdrive (200ohm to 500 ohm?),
or should I start bij increasing the R50 (from 47K to 100-330K?).

[R.G.]

update: squeeling noise is fixed, the trimpot on R35/R36 was a 500 ohm trimpot instead of 200k. I just used 2 x 100K resistor and now I have a normal signal.

Ah. That is a hard one to find by any method except on-site, exhaustive search.

No effect yet because the lamp is just glimmering (not enough voltage on that one I guess).

I'm guessing that "glimmering" means "only getting a little dimmer and brighter, not going nearly off".  This is most likely a bias problem on the lamp driver.

Is it better to use a larger trimpot on the lampdrive (200ohm to 500 ohm?),
or should I start bij increasing the R50 (from 47K to 100-330K?).

And the trimpot in the driver's emitter is the first place to look.  You should be able to turn the lamp down to nearly off with the trimpot. If that's not true, check carefully all the component values R47, R48, R49, R50, and the value of the trimmer pot. Even with depth turned fully down, the trimpot should change the lamp brightness down to nearly off, and up to bright, if not full brightness.

[larsthestrat]

thanks!

Lamp is 'just' glimmering and turned off really quickly when turning the trimpot (200 ohm), no change when turning speedknob/depthknob. No change when using 330K on R50, or 500 Ohm trimpot instead of 200 ohm trimpot.

I also found some strange voltages on Q11/Q12:
Q11 (C,B,E) 19V,16V,19V
Q12 (C,B,E) 19V,19V,19V
the other voltages are almost similar as shown in the schematic (example r39/r40 is 11,1V). Q11/Q12 blown?
I'll check on the components on the lamp driver.

[R.G.]

Divide and conquer.

Remove C23. Do the DC voltages on the lamp driver change at all? If so, C23 was either backwards or leaking.
Measure DC on the depth pot with C23 removed. If any of the voltages on the depth pot are not less than 5mV, then C22 is backwards or leaking.

Once you get this done, we can look at the LFO. It appears to have its emitter path open, but don't go splitting your attention.

[larsthestrat]

after removing c23 the measurements on Q13 remained the same (a little bit smaller). Voltages on the depth pot are changing fast, but from 0 to 12mV (on the right lug and middle lug), left lug remained at 0.05mV.
I hope I measured correctly. Parts are
R47 = 100K
R48 = 68 ohm
R49 = 4K7
R50 = 330K (just for now)
trimpot = 200 ohm

[R.G.]

after removing c23 the measurements on Q13 remained the same (a little bit smaller). Voltages on the depth pot are changing fast, but from 0 to 12mV (on the right lug and middle lug), left lug remained at 0.05mV.

When you say "remained the same", what were those voltages?
(they tell me what the transistor is doing)

I hope I measured correctly. Parts are
R47 = 100K
R48 = 68 ohm
R49 = 4K7
R50 = 330K (just for now)
trimpot = 200 ohm

No obvious problems. R49 can vary and have it work OK. Some production Univibes had a 68 or 75 ohm resistor for R48 and no trimpot at all.

The voltages will help me figure it out. What is the voltage and either current or power rating of your lamp?

[larsthestrat]

the voltages on Q13 were exactly the same with en without the C23 cap in. you did mean C23?
This lamp has the following specs: 6-12V, 20-40mA

nb. I have to buy a new one, this one snapped of.

[R.G.]

Did some thinking. If the wiper of the trimpot was open, it might cause exactly these symptoms.

Turn the power to the unit off, then clip your meter set to "ohms" between the emitter of Q13 and ground. Measure ohms between the emitter and ground as you turn the trimpot. You should be able to get resistances down to the 68 ohms and up to 200+.  If not, there is something funny about the pot.

[larsthestrat]

I just checked and it does fluctuate from 68ohm to about 330ohm when turning the trimpot.
Just got the new light bulb (18V), solder that one in?